HideOldRedditFrontpageOldPosts.user.js

// ==UserScript==
// @name         Hide Old Reddit Frontpage Old Posts
// @namespace    https://greasyfork.org/en/users/85671-jcunews
// @version      1.0.3
// @license      AGPLv3
// @author       jcunews
// @description  https://www.reddit.com/r/GreaseMonkey/comments/l5i3mw/request_script_that_removes_hides_stale_reddit/
// @match        https://*.reddit.com/
// @match        https://*.reddit.com/?*
// @match        https://*.reddit.com/hot/*
// @match        https://*.reddit.com/new/*
// @match        https://*.reddit.com/rising/*
// @match        https://*.reddit.com/controversial/*
// @match        https://*.reddit.com/top/*
// @match        https://*.reddit.com/gilded/*
// @grant        none
// ==/UserScript==

((ele, link) => {

  var maxAgeHours = 20;
  var maxUpVotes  = 100;
  var maxComments = 50;

  if (!(ele = document.querySelector(".tabmenu"))) return;
  ele.appendChild(link = document.createElement("A")).textContent = "[Hide Olds]";
  link.style.marginLeft = "1em";
  link.href = "#";
  link.onclick = () => {
    var now = new Date;
    Array.from(document.querySelectorAll(".sitetable .thing")).forEach(
      (post, index) => {
        var
          posttime = new Date(parseInt(post.dataset.timestamp)),
          eleVotes = post.querySelector(".score.unvoted"),
          comments = post.dataset.commentsCount,
          eleHide = post.querySelector(".hide-button a");
        if (isNaN(posttime) || !eleVotes || !comments || !eleHide) return;
        if (
          ((now - posttime) > maxAgeHours * 60*60*1000) ||
          (parseInt(eleVotes.title) > maxUpVotes) ||
          (parseInt(comments) > maxComments)
        ) eleHide.click()
      }
    );
    return false
  }
})()